TRANSITION FROM FERNS TO FLOWERS 113 



in greenhouses. But there are yet other cases among 

 fern-like plants, in which the big spores mentioned above 

 actually germinate without quitting the leaflet on which 

 they are formed and produce very minute prothalli bearing 

 egg-pits without separation from the spore-bearing fern ! 

 Now, it is no stretch of the imagination to conceive of fern- 

 like plants as having once existed, in which the leaflets 

 bearing large spores should be grouped like the scales of a 

 pine-cone or the whorls of a flower so as to protect the 

 large spores, and that these spores should " germinate " 

 beneath their coats each where it is fixed, thus producing 

 without falling from its place of origin a minute, solid, little 

 prothallus, which in due course produces one or more egg- 

 pits, each holding a single egg-cell. Each such leaflet is a 

 carpel or carpellary leaf. At the same time the leaflets 

 carrying the small spores destined to produce prothalli, 

 which will carry only sperm-sacs, must be supposed to 

 have formed either a separate male cone or a male flower, 

 or to have arranged themselves around the female carpels 

 as stamens or staminal leaflets. We shall see what 

 happens to the small spores which they produce. 



How, then, are we to suppose that fertilisation took 

 place ? The extinct plants in which these changes actually 

 arose were not small or aquatic in habit. They were well 

 grown shrubs and trees. This is what occurred. The 

 staminal or male leaflets produced their small spores in 

 spore-cases (the anthers), and the cases burst, setting free 

 the male-prothallus-producing spores, which are, in fact, 

 the same thing as the pollen grains of higher plants. 

 Unlike the female-prothallus-producing spores, or big 

 spores, they do not remain in place, but are shed in 

 showers of millions into the air. They are blown by the 

 wind (as we see to-day in the case of pines and many 

 other trees), and are carried by it to the female or car- 

 pellary cones, or maybe to rosette-like female flowers. 



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